The proposed study is concerned with the role of attention and information-processing in schizophrenia. The two immediate goals of this study are to (1) determine if attentional deficits define a homogeneous subgroup of schizophrenic patients and, therefore, potentially are indicators or markers of a specific subtype of schizophrenia and (2) assess the accuracy with which pre-treatment attentional deficits predict medication responsiveness. A multi-task Continuous Performance Test, tapping a range of attention and information processing skills, will be administered to 40 schizophrenic patients, 20 manics, and 40 normal controls. All subjects will be tested twice. Schizophrenics will be initially tested off-medication (following a 2 to 4 week washout) and will then be retested after a standardized 6-week prospective haloperidol treatment phase. Schizophrenics will be classified into attentionally deviant vs non-deviant subgroups on the basis of their baseline attentional performance levels and the two subgroups will be compared on a number of clinical and background variables. The schizophrenic group will then be reclassified into treatment responsive and treatment refractory subgroups on the basis of their clinical course over the six week treatment phase. The two treatment groups will be compared for differences in deficit profiles. This design will enable attentional processing and drug responsiveness to be examined first independently and then interactively. All 20 manic patients will be initially tested while in an acute episode and then retested in remission to (1) assess similarities between manics and schizophrenics in attentional deficit profiles and (2) determine whether dysfunctions detected in manic patients are epiphenomenal of illness or are stable traits. Such information is critical for establishing the specificity of attentional deficits to schizophrenia. In addition, 30 of the 40 normal controls will be tested twice, drug-free to provide both normative baseline data essential for interpreting schizophrenic and manic profiles and formation about improvement in retest performances due to practice effects alone. The remaining 10 normal controls will be tested first drug- free and then retested after receiving haloperidol to assess the effects of medication on normal processing patterns.